Re: Changing the default random_page_cost value

On Thu, Oct 24, 2024 at 08:01:11PM -0400, Greg Sabino Mullane wrote:
> On Mon, Oct 14, 2024 at 5:15 PM Bruce Momjian <bruce(at)momjian(dot)us> wrote:
>
> I am not a fan of this patch.  I don't see why _removing_ the magnetic
> part helps because you then have no logic for any 1.2 was chosen.
>
>
> Okay, but we have no documented logic on why 4.0 was chosen either. :)

Uh, we do, and it is in the docs:

Random access to mechanical disk storage is normally much more expensive
than four times sequential access. However, a lower default is used
(4.0) because the majority of random accesses to disk, such as indexed
reads, are assumed to be in cache. The default value can be thought of
as modeling random access as 40 times slower than sequential, while
expecting 90% of random reads to be cached.

You surely saw this when you created the patch and removed the text.

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Bruce Momjian <bruce(at)momjian(dot)us> https://momjian.us
EDB https://enterprisedb.com

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